My vision on how it could be used:
If someone has a question about a package the wiki is thier first stop. It becomes usefull if people have done the following:
1. Developers make note of thier current work and intentions if they are acitve on a package.
2. Developers as you are working on things if you have an insight make a note of it there.
3. Volunteers and newbies, when you find the answer to your question in the forums or from help on IRC etc. make a note of it and/or link to it on the relevant wiki page so that the next person can find it.
Remember this is a wiki not the offical documentation. I think its fine to state your opinions not just the facts. I think opinions are valuable. In OpenACS there is almost always more then one way to do something. We often strong opinions about the right way. Experienced people may not always agree but our disagreements are usually educational and we often agree that newbies do it wrong :).
When should you post in the forum and when should you write in the wiki?
If you want an opinion from a wide range of people or you need an immediate response - use the forums.
If you were sitting next to a teammate who was working on the same package and you'd tell him what you just learned then write that in the wiki. The person who works on that package next month will thank you.